Centering unit for a silk-screen printing device

ABSTRACT

A centering system for a screen printing apparatus includes a platform for the placement of a plate to be printed, abutment wheels arranged on the platform, longitudinally adjustable servo shafts, beams, and a stationary frame on which the beams are arranged. The wheels are configured to contact the outside edges of the plate and secure the position of the plate for further processing. The longitudinally adjustable servo shafts lie above the platform, and the abutment wheels are mounted on the servo shafts. The beams are arranged above the platform, and the servo shafts are mounted beams.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to a centering system for a screen printingapparatus, having abutment wheels arranged in a platform for plates ordisks to be printed, which come into contact with the outside margin ofthe plates or disks and secure their position for further processing.

Centering systems of this kind are known. The positioning of the platesor disks to be printed is accomplished as a rule by urging the platespneumatically against fixed abutment wheels. Tolerances in the plates ordisk dimensions cannot in such a procedure be compensated.

It is also known, however, to couple together oppositely lying abutmentwheels mechanically, e.g., via chain spindles or cogbelts, so that ifthe abutment wheels shift, the confronting abutment wheels will move thesame distance, thus assuring centering on the center of the disk orplate. This procedure permits a compensation of dimensional tolerancesof the disks or plates. What is disadvantageous is the very complicatedmechanical structure, which must be configured so that twisting andshifting of the plates or disks is possible. Also, the abutment wheelsare defined as to their direction of movement by the design. Plates orpanels with certain outside dimensions, e.g., the side panels ofautomobiles, cannot be positioned by such systems.

The invention is based on the task of improving a centering system ofthe kind described above so that with comparatively little expense acentering of plates or disks of any shape on the center of the platformbecomes possible.

To solve the problem the abutment wheels in a centering device of thekind referred to above are applied to longitudinally adjustable servoshafts which lie above the platform level and in turn are applied tosupports which are arranged on a stationary frame and above theplatform. In this configuration centering is possible in a relativelysimple manner; the confronting abutment wheels can be drivensynchronously, so that disk or plate tolerances can be equalized.

Of course, it is also possible to fix some of the abutment wheels inplace if the application should require it. Then the positioning isperformed, in a development of the invention, by detecting the torquesexercised by the servo shafts, which are sensitively detected. When eachabutment wheel comes in contact with the edge of the plate or panel thetorque increases. Thus, by detecting the torque, the position of theplate can also be detected. The result is the possibility of equalizingthe desired and the actual position, so that the centering becomespossible in a simple manner.

In further development of the invention, all records of movement anddetections of position can be stored in a memory, so that they can berecalled in the event of a new print order. The centering force itselfcan be called from memory in the event of a new print order. Thecentering force itself can be adjusted by means of the torque of theservo shafts. It is also possible to transfer plate data to thepositioning system via a CAD system. This eliminates the sensing of theplates by the servo shafts.

In further development of the invention, the servo shafts are mountedswivelingly on the beams so that their direction of action is alsovariable. The beams can have holes arranged at intervals for thispurpose and the servo shafts can be provided with pins which can beanchored in them. In this way adjustments of the axes of action can beperformed without great effort. This may be necessary in the case ofcertain panel or plate forms, as will be explained further on.

In further development of the invention a transport line can be placedbefore the work platform and a conveyor belt running parallel theretocan be provided, by which the plates or panels can be raised by alifting means to the platform. This lifting means can be advantageouslyprovided with a plurality of ball guides lying in one plane, which canbe lifted together above the plane formed by the conveyor belt to theplatform. The plates or panels then lie on the ball guides and can beadjusted easily to the desired centering position by operating the servoshafts.

The abutment wheels are best spaced away from the servo shafts. They canbe arranged on the servo shafts at variable distances apart, swivelinglyfor example, so that in order to contact the external contours of thepanels or plates they can be turned downwardly to the working position.

It is also possible, however, to mount the abutment wheels with theirshafts fixedly on the servo shafts and to arrange the beams for theservo shafts for raising and lowering together on the frame. Thisconfiguration assures greater strength and thus more stable arrangementof servo shafts and abutment wheels. The lifting movement of the beamsystem itself offers no difficulty. It can be configured, for example,in a manner similar to the way provided for raising and lowering inscreen printing machine superstructures.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is represented in the drawing by examples of itsembodiment and is explained hereinafter.

FIG. 1 is a front view of a centering apparatus of the invention.

FIG. 2 is a plan view of the apparatus of FIG. 1, but without thetransport section.

FIG. 3 is a side view of the centering apparatus of FIG. 2, seen in thedirection of the arrow III.

FIG. 4 to FIG. 7 are views of the action in time of the feeding, thealignment and the further transport means of a plate or disk to beprinted in screen printing machine that follows.

FIG. 8 is an enlarged detail of a centering device according to theinvention, in an embodiment different from the embodiment in FIGS. 1 to3.

FIG. 9 is the representation of a section taken in the direction of theline of section IX-IX in FIG. 8.

FIG. 10 is a schematic drawing of a centering procedure in a firstembodiment.

FIG. 11 is the view in the direction of the arrow XI of FIG. 10.

FIG. 12 is a view similar to FIG. 10, but in the case of the centeringof a plate or disk with external contours different from those shown inFIG. 10.

FIG. 13 is a view similar to FIG. 12, but for centering an additionalshape of plate or disk.

DETAILED DESCRIPTION OF THE DRAWINGS

FIGS. 1 to 3 show a centering system 1 which has a frame 2 which can beplaced on a floor not shown, and in which plates 3 can be centered inthe manner to be explained hereinafter. The centering system 1 is placedin front of a transporting system 4 with a roller train on which theplates 3 can be fed to the centering system 1 in the direction of thearrow 6.

Within the frame 2 a carrier frame 7 having four crossbeams 8 adjoiningthe transporting system 4, each equipped with four upwardly facing ballguides 9. The ball guides 9 or their uppermost points lie in a commonplane. The ball guides 4 therefore support the plate 3 in the positionshown in FIGS. 1, 2 and 3 of the centering system 1. FIG. 4 makes itclear that, in a starting position, namely when the plate 3 isintroduced in the direction of the arrow 6 into the centering system 1,the frame 7 lies with the ball guides 9 underneath the plane oftransport of the plate 3 which is taken by a conveyor belt 10 not shownin FIG. 1 but seen in FIGS. 2 and 4, and carried into the centeringsystem 1. When this is done, then the frame 7 is raised to the levelseen in FIGS. 1 and 3, so that the ball guides 9 together form a workplatform 12 for the plate 3.

In the frame 1, above this work platform 12, a carrier system in theform of a frame with three beams perpendicular to the crossbeams 8 isprovided and can be seen in FIG. 8 and the following figures. On thesebeams lying at the top surface of the frame 1 and underneath the frame1, so-called servo shafts 14, 14 a and 14 b, and 15 and 15 a, are soarranged that the bars which surround corresponding adjusting spindleslike housings lie beneath the beams 13. The holding bars 16 for theseservo shafts are fastened each to angle bars 17 of supports 13, which inturn are fastened to crossbeams 18 at the upper edge of frame 1. FIGS. 8and 9 make it clear that the guiding housings 16 are held on the beams13 by U-shaped clamping devices 19 with tommy screws and by pins 21engaging in holes 20 in the bars 17. Each servo shaft is provided in aknown manner with an adjusting spindle and with an electrical drive 22with which it is possible to shift a mount 23 (FIG. 9), carried on a nuton the spindle, between a first end position 23 a and a second endposition 23.

The supports 23 are each provided with abutment wheels 24 which in thecase of the embodiment in FIGS. 8 and 9 are disposed with their axestight against the support 23 but are themselves made able to rotate.

In the embodiment in FIGS. 1 to 3 the abutment wheels 24 are indeedconnected likewise with a support displaceable on the servo shafts 14,15, but there, by means of levers 25 not shown, the abutment wheels 24can be removed upwardly from the level of the work platform 12 withoutthe need to move the servo shafts 14 and 15 for that purpose.

The embodiment in FIGS. 8 and 9, which is also retained in the followingFIGS. 10 to 13, provides, as it can also be seen from the drawings, thearrangement of the abutment wheels 24 on much shorter guides. Thearrangement is thereby made more stable, but it assumes that the servoshafts 14 and 15 including their supports 13 and the support systemassociated with them, can be raised upward so as not to interfere withthe introduction of the plates 3 when they are entering the centeringdevice (see FIG. 4). The raising of the support system for the servoshafts 14 and 15 can be accomplished in the same manner as is the casewith the upper mechanisms of screen printing machines, one of which—notshown—follows the centering system 1 in the direction of arrow III (FIG.2).

It is now going to be explained, with the aid of FIGS. 4 to 7, how thecentering of the plates 3 in the centering device 1 takes place, and howthe further transport of the centered plates to the screen printingmachine, not shown, is carried out.

First, FIG. 4 shows how, as already indicated, when the plate 3 isintroduced into the centering system, both the ball guides 9 and theabutment wheels 24 are raised and lowered from the support plane 14lying at the bottom edge of plate 3. When the plate 3 has reached thecentering system, the ball guides 9 are raised up so that, as explainedpreviously, they form the platform 12 for the plate 3 which thus nolonger lies on the conveyor belt 10. Then the abutment wheels 24 aremoved into the platform 12 which is accomplished either in theembodiment of FIGS. 1 to 3 by turning down the lever 25, or in theembodiment of FIGS. 8 and 9 by lowering the support 13.

The servo shafts 14 and 15 are then operated until the abutment wheels24, as shown in FIG. 5, engage the outside contour of plate 3 and holdit. This position is held fast because a pick-up device is provided todetect the torque of the motors 22 driving the servo shafts 14, 15,which can be accomplished, for example, by detecting the currentrequired for the operation of the motors 22. Such a pick-up device canoperate very sensitively, so that, in the event of a correspondingincrease in the torque, the thereby established position of plate 3 inthe centering device is unerringly detected and makes a precisecentering of plate 3 possible by matching the set and the actualpositions, which is independent of any tolerances in the contour of theplate 3. The detected values of this reached end position can also bestored in a memory and called back again for the centering of asubsequent plate.

It is also possible, however, to dispense with the detection of thetorque and the resultant storing of the determined values if the data onthe plates to be printed are known. The possibility consists, known fromother systems, of transferring these plate data by means of a CAD systemdirectly to the positioning system and storing them.

FIG. 6 shows that the plate 3 is seized in its centered position by atransporting means 26, suction cups 27 for example, and carried in thedirection of arrow 6 from the centering system to the screen printingmachine, which is not represented. These steps are shown in FIG. 6 wherethe suction cups 27 of the transport means 26 become active before theabutment wheels 24 are removed from the plate 3. FIG. 7 shows that thenthe abutment wheels 24 and the ball guides 9 are removed from the plate3 and from the platform 12 so that the plate 3 can be moved in thedirection of arrow 6 to the screen printing machine not shown, whichfollows in the direction of arrow III of FIG. 2. Thereafter delivery ofanother plate 3 takes place as in FIG. 4.

FIG. 8 and FIGS. 10 to 13 show examples of plates 3, 3 a, 3 b and 3 cwith different external contours which can be centered without problemsby the system of the invention. FIG. 8 shows first that the servo shafts14 and 14 a are parallel to one another between the adjacent supports13, and that the servo shaft 14 b is arranged parallel thereto on theopposite side. Not shown are servo shafts disposed perpendicular theretowhich serve to form a stop across the direction of movement of the servoshafts 14, 14 a and 14 b.

The square plate 3 shown in FIG. 8 can be centered at the center pointof the centering system by the operation of the servo shafts. Theabutment wheels 24 of the three servo shafts are for this purpose urgedfrom opposite sides against the outer edges of the plate 3. In likemanner abutment wheels 24 are urged against the sides of plate 3 whichare contacted by the abutment wheels 24 of the servo shafts 14 a and 14b. FIG. 8, however, also makes it clear that plates up to size 3′—seethe diagonal lines 29—can be centered in the system if this should benecessary. It is also possible, as indicated in broken lines, to arrangethe servo shafts 14, 14 a or 14 b at an angle to the beam 13 byinserting pins 21 or additional pins 28 into corresponding holes 20 inbars 17 and the servo shafts are then fixed in this position by theirclamping devices 19. This possibility opens the centering of plates 3, 3a, 3 b, 3 c and of plates or disks with still other external contours ina relatively simple manner, which was not possible heretofore.

FIG. 10 shows the centering of a plate 3 a with round shapes on oneside. Here the centering is performed basically in the same manner asrepresented in FIG. 8. In their direction of action, the servo shafts14, 14 a and 14 b engage opposite sides of the plate 3 a, while servoshafts 15, 15 a, urge their contact wheels 24 in a perpendiculardirection of action against the outside contour.

In FIG. 12, where only two external edges perpendicular to one anotherare present, servo shafts 14 and 14 a press in one direction against theouter contour 31 of plate 3 b, while one servo shaft 14 b is directedapproximately perpendicularly against the curvilinear outside contour 32of plate 3 b, and an additional servo shaft 15 is aimed perpendicular tothe direction of action of the servo shafts 14 and 14 a. It becomesclear that with such an arrangement and the corresponding contact of theabutment wheels 24 the plate 3 b can be fixed perfectly in its position,and in fact centered, so that any tolerances in the outside contourshave no influence on the centered position.

Lastly FIG. 13 shows a plate 3 c with a recessed edge 33 against whichtwo abutment wheels 24 of servo shafts acting parallel to one anotherare placed. The abutment wheel 24 of one servo shaft 14 b acts againstit, and the lateral centering is performed by the abutment wheels 24 ofservo shafts 15 and 15 a, of which one runs perpendicular to thedirection of action of servo shaft 14 b, the other at an angle to thedirections of action of the other servo shafts. The corresponding servoshaft 15 a then lies with its abutment wheel 24 against the curvilinearoutside edge of plate 3 c.

The examples shown therefore make it clear that, with the systemaccording to the invention, all plate shapes can be centered.Complicated mechanical designs are not necessary. The positioning isperformed in each case by electrical drives and by a correspondingcontrol thereof, while, as indicated above, a set value and actual valuecan be adjusted in order to reach the precise alignment position.

In the above description of the embodiments, it is the centering ofplates that is always involved. As explained in the beginning, plates,for motor vehicles for example, can also be centered in this manner andthen can be imprinted by the screen printing method, if this isnecessary. The expression “plates” is therefore also to be understood inthe sense of panes or panels.

1. A centering system for a screen printing apparatus, comprising: aplatform for the placement of a plate to be printed; abutment wheelsarranged on the platform, which wheels are configured to contact theoutside edges of the plate and secure the position of the plate forfurther processing; longitudinally adjustable servo shafts on which theabutment wheels are mounted on and which lie above the platform; beamson which the servo shafts are mounted and which are arranged above theplatform; and a stationary frame on which the beams are arranged.
 2. Thecentering system according to claim 1, wherein the servo shafts aremounted swivelingly on the beams so that their directions of action areadjustable.
 3. The centering system according to claim 2, furthercomprising a motor for driving each servo shaft, wherein the torque ofeach motor is monitored and used for determining the plate position. 4.The centering system according to claim 3, wherein the magnitude of thetorque and the drive for each servo shaft are recorded recoverably in amemory unit.
 5. The centering system according to claim 4, wherein atransport line is placed before the platform and a conveyor belt runningparallel to the platform is associated with the transport line, andwherein the plate can be raised to the platform level.
 6. The centeringsystem according to claim 5, further comprising a plurality of ballguides lying in one plane, which ball guides can be lifted togetherabove the level formed by the conveyor belt to the platform level,wherein the plate is raised on the ball guides.
 7. The centering systemaccording to claim 1, wherein the plate dimensions are received througha CAD system for controlling positions of the servo shafts.
 8. Thecentering system according to claim 1, wherein at least one of the beamsincludes holes arranged at intervals and at least one of the servoshafts includes a pin which can be anchored in one of the holes.
 9. Thecentering system according to claim 1, wherein the abutment wheels standapart unilaterally from the servo shaft axes.
 10. The centering systemaccording to claim 9, wherein the abutment wheels are adjustable indistance along the servo shafts.
 11. The centering system according toclaim 10, wherein the abutment wheels are disposed for swiveling at theservo shafts.
 12. The centering system according to claim 11, whereinthe plate dimensions are received through a CAD system for controllingpositions of the servo shafts and stored in memory.
 13. The centeringsystem according to claim 9, wherein the abutment wheels are mountedwith their axles fixedly on adjustable mountings of the servo shafts andwherein the supports for the servo shafts are part of a raisable andlowerable frame which is provided at the top side of the stationaryframe.
 14. The centering system according to claim 1, further comprisinga motor for driving each servo shaft, wherein the torque of each motoris monitored and used for determining the plate position.
 15. Thecentering system according to claim 14, wherein the magnitude of thetorque and the drive for each servo shaft are recorded recoverably in amemory unit.
 16. The centering system according to claim 15, wherein atransport line is placed before the platform and a conveyor belt runningparallel to the platform is associated with the transport line, andwherein the plate can be raised to the platform level.